Summary of work: Previous research in this Laboratory and elsewhere has shown that in American samples, mean levels of some personality traits decline whereas others increase in the decade of the 20s. Cross-sectional replications suggested that this might be a universal phenomenon. A pan-cultural test of that hypothesis was conducted using data from 26 cultures from five continents. Compared to older adults, college-age respondents around the world scored higher in Neuroticism, Extraversion, and Openness to Experience, and lower in Agreeableness and Conscientiousness. These cross-sectional findings were replicated in longitudinal analyses of an American sample for Neuroticism, Extraversion, and Openness, but Conscientiousness unexpectedly declined. Further research is needed to account for this anomaly. Both cross-cultural and longitudinal studies on personality, stress, and coping will continue.